Metals and articles containing metals typically undergo some form of oxidation when exposed to air and moisture. Iron and iron alloys are particularly prone to corrosion, which if allowed to proceed, detracts from the appearance of the article and can penetrate deeply into the metal to impair its mechanical properties. Most other metals also corrode upon exposure to water and air, although to different extents. For example, aluminum corrodes to produce white specks, while copper corrodes to produce a bluish-green coating. The layer of corrosion on aluminum and copper typically does not penetrate through the metal, although it can affect the desired properties of the metal. In electrical components, for example, even small amounts of corrosion between electrical contacts can result in failure of the components.
It is customary to protect metal parts against corrosion by applying a protective film. Examples of protective coatings which have been extensively used include petroleum base grease-like compositions, plastic compositions such as proxylin type films, and asphalt base varnishes. The grease-like compositions have been found unsatisfactory for many uses due to the poor resistance to abrasion and the low temperature melting encountered during use of the coated article. The asphalt varnishes and plastic coatings provide adequate protection against corrosion although the coatings are difficult to apply and difficult to remove from the metal surfaces. The decomposition of some of these coating compositions may result in free acids which can react with the metal.
A major use of coating compositions is in the prevention of rust on steel, such as automobile bodies. Some processes of applying a corrosion resistant coating use a wax material which is applied to the steel parts. It is generally desirable to form a wax coating of a predetermined thickness on every area of the surface subject to the treatment. Furthermore, the composition must penetrate into narrow spaces of the work piece. The coating composition requires a low viscosity to penetrate the areas to be protected. Low viscosity waxes can be difficult to apply and are difficult to apply in the desired thickness. To achieve the desired thickness, successive dippings in the coating material are required. The dipping process, however, does not permit selective application of the material.
Numerous coating compositions are known to be applied as coatings or protective films to prevent the penetration of air and water. Examples of some of these compositions are disclosed in U.S. Pat. No. 4,477,281, U.S. Pat. No. 3,641,551 and U.S. Pat. No. 4,021,262. Wax treatments using mechanical force to achieve penetration of the wax into the interstices of the article is disclosed in U.S. Pat. No. 4,606,945.
The coating compositions are often difficult to apply and difficult to produce. Many of these compositions further fail to provide adequate penetration into tight spaces and fail to provide a uniform coating.